Toward Sustainable Fertilization: Biochar and Plant Growth Promoting Bacteria (PGPB) Influence on Sweet Pepper (Capsicum annuum L.) Development and Production Under Reduced Nitrogen Input

Soil amendment with biochar and PGPB represents a promising strategy to reduce dependence on chemical fertilizers. This study aimed to evaluate the potential of biochar and PGPB application, under a reduced nitrogen fertilization, to sustain sweet pepper growth and production, soil chemical and microbiological fertility. Plants were grown in pots under greenhouse on soil un-amended or amended with 2% biochar (B0 and B2), un-inoculated or inoculated with PGPB (P0 and P+) and un-fertilized or fertilized with 50 (half dose) or 100 (full dose) kg N ha−1 (N0, N50 and N100). Plant above- and below-ground biomass development, soil chemical and microbiological properties, and fruit quanti-qualitative traits were assessed during and/or at the end of two periods: from transplanting (T0) to flowering initiation (T1) and from flowering initiation to harvest (T2). Under B2-P+ treatment, N50 fertilized plants exhibited growth similar to N100, with 50% higher height and more than doubled leaf number compared with N0. At T2, the Absolute Growth Rate of plant height increased by 12% under B2 compared with B0, by 45% under P+ compared with T1, while the Absolute Growth Rate of leaf number was 60% higher under B2 compared with T1. Biochar and PGPB resulted in higher N tissue concentrations (+66 and +34% in stem; +16 and +11% in leaves, respectively), root length (+27%) and biomass (+170%), respectively. At soil level, B2 increased carbon and nitrogen contents by 94% and 25% compared with B0; P+ resulted in 12% higher carbon content, compared with P-; half N fertilization favoured microbial growth. N50 fertilized plants showed fruit yield, weight, nitrogen and carbon contents comparable to N100. Biochar and PGPB application with half N dose maintained pepper growth and yield at levels comparable to full N fertilization, while improving soil fertility and exerting a modulatory effect on specific soil bacterial families.